Posterior cruciate ligament, PCL, injuries are more common than what had been previously thought. A review of the literature also indicates that multiple ligamentous injuries represent a common reported clinical problem associated with PCL injury; a high incidence of associated injuries is found to occur either in the medial collateral ligament, MCL, or in the lateral compartment including the posterior capsule, PC, and the lateral collateral ligament, LCL. Yet, treatment of PCL injuries remains controversial, especially in relation to the effects of these injuries on the patello-femoral joint. While the literature includes many reports on how well those with PCL injuries do without surgery, more recent reports indicate that a large number of such patients develop significant disability due to the development of tricompartmental degenerative changes and concluded that early repair is the method of choice. These recent reports point out that the posterior sag of the tibia that results from a PCL injury puts increased pressure on the patella, resulting in patellar pain. It seems that most reports of PCL insufficiency have addressed the problem of functional instability, but few have emphasized the potential for early degenerative arthritis. All of these reports have not yet been confirmed or substantiated by means of biomechanical studies. This grant application is directed toward the determination of the changes in patello-femoral tracking patterns (patello-femoral motions) and patello-femoral contact characteristics that follow isolated and combined PCL injuries. The specific aims are to determine how patello-femoral motions and contact characteristics are altered following: 1) isolated PCL injury, 2) combined injury of the PCL and MCL, 3) combined injury of the PCL, LCL and PC. We expect our research to clarify the indications for repair of a torn PCL and provide a better understanding of the mechanism by which abnormalities in patello-femoral motions and joint contact ensue from isolated and combined ruptures of the posterior cruciate. In this project, patello-femoral motions and pressure distributions will be determined concurrently in cadaveric specimens during a simulated flexed knee stance which occurs in various activities of daily living. Our experimental design allows us to determine the influence of different load levels applied to the quad. The methods employed include a complete determination of the three-dimensional patello-femoral motions. Contact characteristics will be determined using two methods: direct and indirect. Contact areas, locations and stresses will be determined directly by using a digital image processing technique to analyze Fuji-film contact prints. Joint contact will also be determined indirectly by combining kinematic data (describing knee motions and geometric data describing joint geometry to determine contact areas and locations; contact stresses will then be calculated via a mathematical model.